Mechanism And Energetic Efficiency Characteristic On Excess Sludge Disintegration By High Pressure Jet Impingement

As the primary method for sewage treatment in the world,activated sludge process will generate a lot of excess sludge during the operation.Improper treating of excess sludge can cause secondary environmental pollution.The excess sludge disinteragation is an efficient pre-treatment method for sludge reduction,harmlessness,resource recovery.The excess sludge floc and bacterial cell wall is an important factor to limit the excess sludge disintegration.Using of effective methods to disintegrate sludge floc and bacterial cell can help to decrease floc intensity and release nutrients from sludge,and thus achieve to the reduction and resource recovery of excess sludge easily.In this study,a high pressure jet impingement flow method was used to crack sludge.Research on the impact of various factors such as jet impact time,spray impingement distance,jet impingement way,impact pressure injection,sludge concentration and nozzle types on sludge cracking.Disintegration of sludge analyzed by and represented by suspension solids concentration(MLSS),the solubility of the chemical oxygen demand(SCOD),protein,peptidogly,ammonia nitrogen(NH4+-N),the sludge particle size,temperature,pH,and etc.Univariate results showed:Sludge crack effect increased with the striking extension of time,but the increasing rate decreased;Increasing of the striking distance impact can improve the effect of cracks in a certain range,but the effect of cracks would drop when it beyond the critical distance.Optimal crack effect occurs in about 5 cm;The collision of treatment effect is better than striking with the wall.Increasing the pressure can increase the impact cracked effect,while the effect of increasing trend showed a temporary standstill when the pumping is around 2500 psi;MLSS boosted up to enhance the effect of crack within a certain range,but the cracks effect is reduced outside of this range.Optimal break concentration is 6000?8000 mg/L.The best nozzle in this treatment is self-oscillating nozzle.Through response surface method test we obtain two mathematical models without considering energy efficiency.Parameters are as follows:time of 24 min,pressure of 3000 psi,spray distance of 6.6 cm.At this point SCOD concentration increments 2335.76 mg/L;time of24min,pressure of 3000 psi,spray distance of 7 cm.At this time the protein concentration increment is 1419.88 mg/L.In the case of considering energy efficiency,we also obtain two mathematical models.Parameters are as follows:time of 7 min,pressure of 1004 psi,spray distance of 7.5cm,at this point SCOD energy efficiency ratio is 1.092×10-3mg/(L·J);time of 5 min,pressure of 1000 psi,spray distance of 5 cm,at this point protein concentration energy efficiency ratio is 7.171 ×10-4 mg/(L·J).Research on the impact of the high-pressure injection process,It was different from the impact,impact pressure and impact mode conditions simulation.And the simulation results are compared with experimental results to analysis of high pressure jet impingement mechanism to crack the remaining sludge.The study also reproduced the deflection hit turbulence in the stream.Striking distance of 1 cm oscillation cycle time is 4.7420×10-6 s,striking distance of 5 cm oscillation cycle time is 1.2858×10-4 s,and striking distance of 9 cm oscillation cycle time is 1.7995×10-4 s.The study found high-pressure jet impingement ultrahigh pressure treatment sludge is mainly formed by impact or large shearing force.Increasing the impact of the original pressure and divergence appropriate increasing in jet effect can improve crash cracked.